Nonwoven protective fabrics with conductive fiber layer

ABSTRACT

Nonwoven barrier laminates are provided having a desirable balance of properties, including barrier properties, strength, static dissipation, fluid repellency, aesthetics and tactile properties. The nonwoven barrier laminates of the invention generally include outer spunbonded layers, at least one hydrophobic microporous layer between the outer spunbonded layers, and at least one discrete layer of electrically conductive strands. A multiplicity of discrete bond sites bond the various layers of the nonwoven barrier laminate into a coherent fabric.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. provisional patentapplication No. 60/420,496 filed Oct. 23, 2002.

FIELD OF THE INVENTION

The present invention relates to nonwoven fabrics and to processes forproducing nonwoven fabrics. More specifically, the invention relates tononwoven barrier fabrics having a balance of liquid repellent andantistatic properties that are particularly suited for medicalapplications.

BACKGROUND OF THE INVENTION

Barrier fabrics have been developed which impede the passage of bacteriaand other contaminants and which are used for disposable medicalfabrics, such as surgical drapes, disposable gowns, sterile wrap and thelike. Barrier fabrics can be formed by sandwiching an inner fibrous webof thermoplastic meltblown microfibers between two outer nonwoven websof substantially continuous thermoplastic spunbonded filaments. Thefibrous meltblown web provides a barrier impervious to bacteria or othercontaminants in the composite nonwoven fabric. The outer spunbonded websare selected to provide abrasion resistance and strength to thecomposite fabric. Examples of such trilaminate nonwoven barrier fabricsare described in U.S. Pat. Nos. 4,041,203 and 4,863,785.

However, in addition to barrier properties and strength, medical barrierfabrics must also advantageously provide a number of other beneficialproperties. For example, barrier fabrics used in medical applicationsmust dissipate static charge because they are often used in the presenceof sensitive electronic equipment and potentially volatile gases such asether. Medical barrier fabrics must also exhibit superior fluidrepellency, so that contact by water, alcohol or other organic solventsdoes not impair the barrier properties of the fabric.

Both static dissipation and fluid repellency have generally beenimparted to medical barrier fabrics to date by applying a series oftopical treatments. More specifically, antistatic performance has beenimparted to medical fabrics by the application of hydrophilic coatings.Fluid repellency has been achieved in medical fabrics by the applicationof hydrophobic coatings. Unfortunately, the hydrophilic and hydrophobicnatures of the various topical treatments are incompatible, hence thebalance of properties provided to the barrier fabric is generallycompromised. For example, acceptable antistatic performance may beachieved at the sacrifice of water resistance.

Fabrics rendered antistatic by means other than topical treatments areknown. For example, U.S. Pat. No. 5,368,913 to Ortega disclosesspunbonded fabrics for use in carpeting and the like that includeconductive filaments, such as carbon or metallic filaments, distributedthroughout the fabric thickness. Such fabrics can be problematic ingarment applications because the electrically conductive fiber is notisolated visually or tactilely from the wearer. Conductive filaments,such as carbon or metallic filaments, are not readily dyeable and arethus generally considered to be less aesthetically pleasing than moretraditional textile fibers. Carbon and metallic filaments further lackthe flexibility and softness provided by traditional textile fibers.Further, fabric constructions including conductive filaments throughouttheir thickness generally require a significant amount of conductivefilament, resulting in increased costs. The presence of conductivefilaments during web manufacture can further disable the electrostaticcharges frequently applied to filaments to enhance the uniformity ofnonwoven webs.

Thus there remains a need in the art for improved antistatic, fluidrepellent barrier fabrics.

SUMMARY OF THE INVENTION

The invention provides nonwoven barrier laminates having a desirablebalance of properties, including barrier properties, strength, staticdissipation, fluid repellency, aesthetics and tactile properties. Thenonwoven barrier laminates of the invention generally include outerspunbonded layers, at least one hydrophobic microporous layer betweenthe outer spunbonded layers, and at least one discrete layer ofelectrically conductive strands. A multiplicity of discrete bond sitesbond the various layers of the nonwoven barrier laminate into a coherentfabric.

The nonwoven barrier fabrics of the invention have excellent barrierproperties, provide alcohol and water repellency, antistaticperformance, are readily dyeable, are flexible and comparatively soft.The nonwoven barrier laminates of the invention can be used ascomponents in a variety of nonwoven products, and are particularlyuseful in medical fabrics, such as sterile wraps, surgical gowns,surgical drapes, and the like. The spunbonded layers provide goodabrasion resistance, strength and aesthetic properties to the laminatefabrics of the invention. The inner hydrophilic microporous layerprovides good barrier properties. The layer of electrically conductivestrands provides superior static dissipation characteristics fornegative charges.

In another aspect of the invention, medical fabrics that include thenonwoven barrier laminate described above are also provided. Forexample, the nonwoven barrier fabrics of the invention are useful ascomponents in medical fabrics such as surgical drapes and gowns. Whenused to form a surgical gown, the discrete layer of conductive filamentsdissipates negative static charges as they arise, thereby decreasingboth static discharge and static cling. Accordingly, the surgical gownsof the invention are formed from fabrics having greater safety andcomfort, as well as superior fluid resistance and antistatic properties.

Nonwoven barrier laminates according to the invention can be readilymanufactured according to another aspect of the invention. The nonwovenbarrier fabrics may be manufactured by forming a layered web includingouter spunbonded layers sandwiching at least one hydrophobic microporouslayer and a discrete layer of electrically conductive strands.Thereafter, the layers of the resultant composite laminates aresubjected to a thermal bonding treatment sufficient to introduce aplurality of discrete thermal bonds that provide cohesion to thelaminate.

The nonwoven barrier laminates of the invention provide severaldesirable and yet apparently opposing properties in one fabric. Forexample, the barrier laminates of the invention provide antistaticprotection without sacrifice to fluid repellency.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings which form a portion of the original disclosure of theinvention:

FIG. 1 a is cut-away schematic perspective view of a laminate nonwovenfabric in accordance with one embodiment of the present invention;

FIG. 1 b is cut-away schematic perspective view of a laminate nonwovenfabric in accordance with a second embodiment of the present invention;and

FIG. 2 schematically illustrates one method embodiment for forming alaminate nonwoven fabric of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described more thoroughly hereinafterwith reference to the accompanying drawings, in which illustrativeembodiments of the invention are shown. This invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein. Rather, this embodiment is providedso that the disclosure will be thorough and complete, and will conveyfully the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout. For purposes of clarity, thescale has been exaggerated.

FIGS. 1 a and 1 b are schematic perspective views of a barrier laminatein accordance with two embodiments of the present invention. The barrierlaminate is designated generally as 10. In the advantageous embodimentsprovided in FIGS. 1 a and 1 b, the barrier laminate 10 is a four plycomposite comprising a conductive layer 12 a or 12 b and at least onehydrophobic microporous layer 14 sandwiched between outer plies 16 and18. In addition to beneficial antistatic and fluid repellent properties,the barrier laminate 10 has good strength, flexibility and drape and maybe formed into various articles or garments such as sterile wraps,surgical gowns, surgical drapes and the like. The barrier properties ofthe laminate 10 make it particularly suitable for medical applications,but the laminate is also useful for any other applications wherein abarrier to contaminants and fluid repellency, as well as a cloth-likefeel and drapeability, would be desirable, such as industrial garments,filtration media, and disposable wipes.

The outer plies 16 and 18 of the barrier laminate 10 may be formed fromany construction capable of providing sufficient strength and cohesionto the resulting barrier laminate 10. Advantageously, outer plies 16 and18 of the barrier laminate 10 are nonwoven webs, such as spunbonded websof substantially continuous nonelastomeric thermoplastic filaments. Thethermoplastic filaments of outer plies 16 and 18 can be made of any of anumber of known fiber forming polymers or polymer compositions.Exemplary polymers include those selected from the group consisting ofpolyolefins such as polypropylene and polyethylene, polyesters,polyamides, and copolymers and blends thereof. The terms “polypropylene”and “polyethylene” are used herein in a general sense, and are intendedto include various homopolymers, copolymers, and terpolymers thereof.The term “polyethylene” is also intended to include any polyethylenesuitable for fiber formation including low density polyethylene, highdensity polyethylene, and linear low density polyethylene. Thethermoplastic filaments of outer plies 16 and 18 may be made from eitherthe same or different polymers. Advantageously, the thermoplasticfilaments of outer plies 16 and 18 are formed from polypropylene.

Outer plies 16 and 18 may be produced using well-known nonwovenprocesses, e.g. spunbonding processes, and may suitably have a basisweight in the range of about 10 gsm to 100 gsm. In advantageousembodiments, the outer plies 16 and 18 have a basis weight ranging fromabout 10 to 25 gsm. The basis weights of outer plies 16 and 18 may beapproximately the same, or may differ. Deniers for spunbondedsubstantially continuous thermoplastic filaments in accordance with theinvention generally range from about 2.0 to 4.0.

The hydrophobic microporous layer 14 may be any layer known in the artto provide barrier properties to laminate structures. In advantageousembodiments, the hydrophobic microporous layer 14 is a nonwoven fibrousweb comprising a plurality of nonelastomeric thermoplastic meltblownmicrofibers. The microfibers can be made of any of a number of knownfiber forming polymers or polymer compositions. Such polymers includethose selected from the group consisting of polyolefins such aspolypropylene and polyethylene, polyesters, polyamides, and copolymersand blends thereof. Advantageously, the microfibers are polypropylenemicrofibers.

The microfibers preferably have an average fiber diameter of up to about10 microns with very few, if any, other fibers exceeding 10 microns indiameter. Typically, the average diameter of the fibers will range from2 to 6 microns. The hydrophobic microporous layer 14 is preferablymanufactured in accordance with the process described in Buntin et al.,U.S. Pat. No. 3,978,185. Such meltblown fibers generally have a denierof about 1.0 or less. The hydrophobic microporous layer 14 can have abasis weight in the range of about 10 to about 80 grams per square meter(gsm), advantageously in the range of about 8 to 20 gsm.

The beneficial embodiment illustrated in FIGS. 1 a and 1 b, the barrierlaminate 10 includes a single hydrophobic microporous layer 14. Inalternative embodiments, the barrier laminate 10 includes more than asingle microporous layer 14. For example, the barrier laminate 10 mayinclude two hydrophobic microporous layers sandwiched between the outerlayers 16 and 18. For embodiments including at least two hydrophobicmicroporous layers, the hydrophobic microporous plies may be the same ormay differ. For example, the hydrophobic microporous layers may differin composition, average denier, or basis weight. The multiplehydrophobic microporous layers may either be positioned immediatelyadjacent to each other or they may be arranged so as to sandwich theelectrically conductive layer (12 a, 12 b).

The electrically conductive layer (12 a, 12 b) is a discrete ply thatincludes electrically conductive strands. As used herein, the term“strand” includes any configuration of fibrous or filamentary materialincluding continuous filaments, staple fibers, tow or any other fibrousconfiguration. The electrically conductive strands within the conductivelayer may be distributed within the discrete ply either anisotropically,i.e. substantially randomly throughout the fabric, as indicated in FIG.1 a by the conductive layer 12 a, or the conductive strands may bearranged in a spaced apart relation from one another in zones extendinggenerally longitudinally of the laminate as indicated in FIG. 1 b by theconductive layer 12 b. Although the strands of the layer 12 b extendpredominantly longitudinally in the machine direction, their location inthe cross-machine direction may vary or fluctuate as the strands loop ordouble upon themselves to form generally longitudinally extending bandsor zones where the strands are deposited. Typically, the conductivelayer 12 a or 12 b is a non-cohesive ply prior to bonding the barrierlaminate 10.

Suitable electrically conductive strands for use in the conductive layerinclude any of the electrically conductive strands known in the art,such as carbon fibers or filaments, metallic fibers or filaments, fibersor filaments made from a polymer that has electrically conductive orsatic-discharging properties, and the like. As used herein the term“carbon fibers or filaments” generally refers to fibers or filamentsmade by heating (or “carbonizing”) precursor organic fibers orfilaments, such as rayon or polyacrylonitrile fibers or petroleumresidues, to appropriate temperatures to convert them to primarilycarbon.

The term “carbon fibers or filaments” also includes fibers or filamentsmade conductive by incorporating carbon into a polymeric fiber orfilament structure, for example, by incorporating a core of carbon intoa hollow polymer fiber or filament or by coating a fiber or filamentwith a sheath made of a composite containing carbon or by otherwisefilling thermoplastic polymer with carbon, and the like.

The term “metallic filaments” refers to fibers made conductive byincorporating a metal into a polymeric fiber or filament structure, andincludes, for example, metal plated filaments, metal-depositedfilaments, metallic strands, and the like.

In advantageous embodiments of the invention, the electricallyconductive strands are multicomponent filaments having at least onenonconductive polymer component and at least one conductive component.The nonconductive polymer component can be made of any of a number ofknown fiber forming nonelastomeric polymer or polymer composition. Suchpolymers include those selected from the group consisting of polyolefinssuch as polypropylene and polyethylene, polyesters, polyamides, andcopolymers and blends thereof. The conductive component may be anymaterial providing sufficient static dissipative properties to theconductive layer. For example, the conductive component can be derivedfrom carbon or metal or other conductive additive. It is also possibleto produce conductive monocomponent filaments by incorporating asuitable conductive melt-additive into the polymer melt duringmanufacture of the filaments.

In advantageous embodiments, the electrically conductive strands aremulticomponent fibers that include at least one nylon component and atleast one carbon component. In beneficial aspects of such embodiments,the electrically conductive strand comprises a nylon filament having oneor more carbon sub-filaments attached to its perimeter, such as a nylonfilament having three carbon filaments attached to its perimeter.Exemplary electrically conductive strands include filaments availablefrom Solutia Chemical Company under the trade names NO-SHOCK™ conductivenylon; from Kanebo Ltd. under the trade name BELLTRON™; and the like.One particularly advantageous electrically conductive strand isNO-SHOCK™ conductive nylon grade 18-2-E3N. Exemplary deniers for theelectrically conductive strand range from about 3 to 36 denier, such asfrom about 3 to 18 denier. In one advantageous embodiment, theelectrically conductive strand is an 18 denier multifilament fiberhaving two 9 denier filaments.

Advantageously, the conductive layer is formed solely of electricallyconductive strands. In alternative aspects of the invention, theconductive layer includes nonconductive strands. In such beneficialembodiments, the nonconductive strands can be made of any of a number ofknown fiber forming polymers and polymer compositions. Exemplarypolymers include those selected from the group consisting of polyolefinssuch as polypropylene and polyethylene, polyesters, polyamides, andcopolymers and blends thereof. The nonconductive strands are includedwithin the conductive layer in amounts that do not interfere with theconductive nature of the layer. For example, the nonconductive strandsmay be included within the conductive layer in amounts of up to 10weight percent, based on the weight of the conductive layer.

The conductive layer (12 a, 12 b) may be formed by any means capable ofdepositing a non-cohesive assembly of strands onto a moving surface. Inbeneficial embodiments, the conductive layer is formed by pneumaticallyassisted means, such as an air gun or air laying headbox.

The basis weight of the conductive layer can vary according to thedegree of antistatic properties desired for the barrier laminate 10. Theconductive layer generally has a basis weight ranging from about 0.01 toabout 1.0 grams per square meter (gsm). In beneficial embodiments, theconductive layer has a basis weight ranging from about 0.05 to about 0.5gsm, particularly from about 0.1 to 0.3 gsm. In one advantageous aspectof the invention, the conductive layer has a basis weight of about 0.23.

Surprisingly, barrier laminates 10 containing relatively small amountsof conductive layer can provide acceptable antistatic properties.Considered on a relative weight basis, the conductive layer generallyconstitutes from about 0.1 to 0.5 weight percent of the barrier laminate10. In advantageous embodiments, the conductive layer forms from about0.2 to 0.4 weight percent of the barrier laminate 10. In one beneficialembodiment, a conductive layer constituting about 0.37 weight percent ofthe barrier laminate 10 provides acceptable antistatic properties.

Layers 12 a or b, 14, 16 and 18 of the barrier laminate 10 can be bondedtogether to form a coherent fabric using techniques and apparatus knownin the art. For example, layers can be bonded together by thermalbonding, mechanical interlocking, adhesive bonding, and the like.Preferably, laminate fabric 10 includes a multiplicity of discretethermal bonds distributed throughout the fabric, bonding layers togetherto form a coherent fabric.

In addition, as will be appreciated by the skilled artisan, barrierlaminate 10 can include one or more additional layers to provideimproved barriers to transmission of liquids, airborne contaminatesand/or additional supporting layers.

Barrier laminates 10 of the invention exhibit a variety of desirablecharacteristics that make them particularly useful as a barrier fabricsin medical applications. The outer plies 16 and 18 are designed toprovide good strength and abrasion resistance to the barrier laminate10. The hydrophobic microporous layer 14 imparts barrier properties. Theconductive layer provides acceptable static dissipation times fornegative charges at no sacrifice to fluid repellency, particularly at nosacrifice to hydrostatic head. The barrier laminates of the inventioncan be further be treated with topical fluid repellents to provideconstructions exhibiting a balance of beneficial properties, includingacceptable antistatic performance at no sacrifice to water and/oralcohol repellancy.

Referring now to FIG. 2, an illustrative process for forming anadvantageous embodiment of the barrier laminate 10 is illustrated. Aconventional spunbonding apparatus 20 forms a first spunbonded layer 22of substantially continuous nonconductive polymer filaments.Advantageously, the nonconductive polymer filaments are polypropylenefilaments. The first spunbonded layer 22 is deposited onto a formingwire or screen 24 which is driven in a longitudinal direction by rolls26.

The spunbonding process 20 involves extruding a polymer through agenerally linear die head or spinneret 30 for melt spinningsubstantially continuous filaments 32. The spinneret preferably producesthe filaments in substantially equally spaced arrays and the dieorifices are preferably from about 0.002 to about 0.040 inches indiameter.

The substantially continuous filaments 32 are extruded from thespinneret 30 and subsequently quenched by a supply of cooling air. Thefilaments are directed to an attenuator 36 after they are quenched, anda supply of attenuation air is admitted therein. Although separatequench and attenuation zones may be employed, it will be apparent to theskilled artisan that the filaments can exit the spinneret 30 directlyinto an attenuator 36 where the filaments can be quenched, either by thesupply of attenuation air or by a separate supply of quench air.

The attenuation air may be directed into the attenuator 36 by an airsupply above the entrance end, by a vacuum located below the formingwire or by the use of eductors integrally formed in the attenuator. Theair proceeds down the attenuator 36, which narrows in width in thedirection away from the spinneret 30, creating a venturi effect andproviding filament attenuation. The air and filaments exit theattenuator 36, and the filaments are collected on the collection screen24. The attenuator 36 used in the spunbonding process may be of anysuitable type known in the art, such as a slot draw apparatus or a tubetype (Lurgi) apparatus.

After the spunbonded layer 22 is deposited onto screen 24, the web moveslongitudinally beneath a conventional meltblowing apparatus 40.Meltblowing apparatus 40 forms a meltblown fibers stream 42 ofnonconductive polymer which is deposited on the surface of thespunbonded web 22 to form a spunbonded web/meltblown web structure 44.Advantageously, the meltblown fibers stream 42 is formed frompolypropylene. Meltblowing processes and apparatus are known to theskilled artisan and are disclosed, for example, in U.S. Pat. No.3,849,241 to Buntin et al. and U.S. Pat. No. 4,048,364 to Harding et al.

In meltblowing, thermoplastic resin is fed into an extruder where it ismelted and heated to the appropriate temperature required for fiberformation. The extruder feeds the molten resin to a special meltblowingdie. The die arrangement is generally a plurality of linearally arrangedsmall diameter capillaries. The resin emerges from the die orifices asmolten threads or streams into high velocity converging streams ofheated gas, usually air. The air attenuates the polymer streams andbreaks the attenuated stream into a blast of fine fibers which arecollected on a moving screen placed in front of the blast. As the fibersland on the screen, they entangle to form a cohesive web.

After the meltblown fibers stream 42 is deposited on the surface of thespunbonded web 22, the spunbonded web/meltblown web structure 44 moveslongitudinally beneath an array of air guns 46 which stretches acrossthe width of the web. For example, one or more rows of air guns 46 mayextend across the width of the web. In advantageous embodiments, the airguns within the array are spaced from about 6 to 12 inches apart.

Each air gun 46 in the array deposits a discrete layer of preformedconductive strands 48, in the form of continuous filaments, provided ona package 54 onto the surface of the spunbonded web/meltblown webstructure 44. The air gun 46 may advantageously be a Lurgi apparatus,commonly employed in spunbonding. However, in contrast to their use inattenuating spundonded fibers issuing from a die, the air gun 46 wouldnot be expected to attenuate the preformed conductive filament, butmerely transport it. The transport air may be directed into the air gun46 by an air supply above its entrance end, by a vacuum located belowthe forming wire or by the use of eductors integrally formed in the airgun. The volume of air required to deposit the conductive filament mayvary depending upon the air gun configuration. Typically, a volume ofair sufficient to achieve a filament velocity of about 1000 to 3000 mpmis employed. Each air gun 46 generally deposits conductive strand ontothe spunbonded web/meltblown web structure 44 at a rate ranging fromabout 1 to 3 grams/minute.

FIG. 2 illustrates the use of an air gun 46 to transport a single end ofconductive strand 52. In alternative embodiments, a single air gun 46may be used to simultaneously deposit multiple ends of conductive strand52 onto the surface of the spunbonded web/meltblown web structure 44. Insuch embodiments, the multiple ends may be fed from packages hung on acreel or the like. In alternative aspects of the invention, theconductive filament may be deposited using a slot die. In furtheralternative aspects of the invention, the conductive filament may beformed in-line by means such as spunbonding or meltblowing.

Spunbonded web/meltblown web/conductive layer structure 50 is nextconveyed by forming screen 24 in the longitudinal direction beneath asecond conventional spunbonding apparatus 56. The spunbonding apparatus56 deposits a second spunbonded nonconductive polymer layer onto thestructure 50 to thereby form a laminate structure 58 comprising aspunbonded web/meltblown web/conductive filament ply/spunbonded webstructure 58. Advantageously, the second spunbonded layer is formed frompolypropylene.

The four-layer laminate 58 is conveyed longitudinally as shown in FIG. 2to a conventional thermal fusion station 60 to provide a bonded barrierlaminate 10. The fusion station 60 is constructed in a conventionalmanner as known to the skilled artisan, and advantageously includescooperating embossing rolls 62 and 64, which may include at least onepoint roll, helical roll, and the like. Preferably, the layers arebonded together to provide a multiplicity of thermal bonds distributedthroughout the laminate fabric. Bonding conditions, including thetemperature and pressure of the bonding rolls, are known in the art fordiffering polymers. For composites comprising a polypropylene spunbondedweb/polypropylene meltblown web/conductive strand ply/polypropylenespunbonded web, the embossing rolls are preferably heated to atemperature between about 120° C. and about 130° C. The laminate is fedthrough the embossing rolls at a speed of about 3 to 300 meters perminute, such as a speed between about 5 and 150 meters per minute.

Although a thermal fusion station in the form of bonding rolls isillustrated in FIG. 2, other thermal treating stations such aultrasonic, microwave or other RF treatment zones which are capable ofbonding the fabric can be substituted for the bonding rolls of FIG. 2.Such conventional heating stations are known to those skilled in the artand are capable of effecting substantial thermal fusion of the nonwovenwebs. In addition, other bonding techniques known in the art can beused, such as hydroentanglement of the fibers, needling, and the like.It is also possible to achieve bonding through the use of an appropriatebonding agent as is known in the art, singly or in combination withthermal fusion.

The resultant barrier laminate 10 exits the thermal fusion station andis wound up by conventional means on a roll.

The method illustrated in FIG. 2 is susceptible to numerous variations.For example, the conductive strand 52 may be deposited directly onto thespunbonded layer 22. In such embodiments, the meltblown fibers stream 42is subsequently directed onto the conductive layer and a secondspunbonded layer applied.

Further, although the schematic illustration of FIG. 2 has beendescribed as forming a spunbonded web directly during an in-linecontinuous process, it will be apparent that the spunbonded webs can bepreformed and supplied as rolls of preformed webs. Similarly, althoughthe meltblown web is shown as being formed directly on the spunbondedweb, and the spunbonded web thereon, meltblown webs and spunbonded webscan both be preformed and such preformed webs can be combined with aconductive filament layer to form the laminate fabric. Alternatively,preformed spunbonded and meltblown webs can be passed through heatingrolls for further consolidation, a layer of conductive filamentsdeposited thereon and thereafter a spunbonded layer may be extruded ontothe surface of the conductive filament layer. Similarly, the four-layerlaminate can be formed and stored prior to bonding.

One or more topical treatments is typically applied to the bondedbarrier laminate 10. Such topical treatments and their methods ofapplication are known in the art and include, for example, alcohol andwater repellency treatments and the like, applied by spraying, dipping,etc. Fluorocarbon chemicals to enhance alcohol and water repellency areknown. One example of such a topical alcohol/water repellency treatmentis the application of Spinrite 150 by Fiber Sciences of Fountain Inc.S.C., a proprietary chemical treatment. It is important that naytreatments applied to the material be low in formaldehyde or othervolatile materials since they will be in close contact with peopleduring most applications.

Additionally, the polymers used in the present invention may bespecifically engineered to provide or improve a desired property in thelaminate. For example, any one of a variety of adhesive-promoting, or“tackifying” agents, such as ethylene vinyl acetate copolymers, may beadded to the polymers used in the production of any of the webs or pliesof the laminate structure to improve inter-ply adhesion. Further, atleast one of the webs or plies may be treated with a treatment agent torender any one of a number of desired properties to the fabric, such asflame retardancy, hydrophilic properties, and the like.

Surprisingly, the barrier laminates of the invention can providesuperior antistatic performance in comparison to conventional antistaticbarrier fabrics. The typical maximum static decay time specified bymedical gown converters is 0.5 seconds or less. The static decay time ofconventional topically treated antistatic barrier laminates ranges fromabout 0.2 to 0.4 seconds. In contrast, the barrier laminates of theinvention are capable of static decay times of about 0.1 seconds,particularly for negative charges. The advantageous antistaticproperties of the invention are further provided at no sacrifice to theremaining laminate properties. In particular, the present inventionimparts antistatic properties to barrier laminates without detrimentallyaffecting the fluid repellent properties of the fabric, especially thewater resistance.

The present invention will be further illustrated by the followingnon-limiting examples.

Comparative Examples 1 Through 5

The antistatic and fluid repellent properties of several polypropylenespunbond/meltblown/spunbond (“SMS”) webs commercially available from BBANonwovens were determined before and after the application of variousantistatic and/or fabric repellent topical treatments. The topicaltreatments were applied to the commercially available SMS byconventional means, such as dip coating. The results set forth in Table1 attached demonstrate the detrimental effect of antistatic topicaltreatments on the water resistance, i.e., the hydrostatic head, ofconventional SMS webs.

Laminates of the Invention EXAMPLES 1 AND 2

Barrier laminates according to the invention were prepared as describedbelow. A first spunbonded web was formed of polypropylene available fromAmoco under the trade designation 7956. The filaments in the firstspunbond layer had a denier per filament of about 2 to 3, and thespunbonded web of substantially continuous polypropylene filaments had abasis weight of about 25 gsm. A meltblown web was prepared bymeltblowing polypropylene available from Exxon under the tradedesignation 3746G to give a fibrous web having a basis weight of about12 gsm onto the surface of the first spunbonded web. A conductive layerwas formed by directing 18 denier Grade 18-2-E3N conductivemulticomponent nylon/carbon filament from Solutia Chemical Company toform a ply having a basis weight of about 0.23 gsm onto the surface ofthe meltblown web. A second spunbonded web formed of polypropyleneavailable from Amoco under the trade designation of 7956 was formed onthe surface of the conductive layer. The filaments in the secondspunbond layer had a denier per filament of about 2 to 3 denier, and thespunbonded web of substantially continuous polypropylene filaments had abasis weight of about 25 gsm.

The webs were bonded together to form a barrier laminate by passing thesample through the nip of a cooperating pair of textured and smoothembossing rolls.

The antistatic and fluid repellent properties of a web formed inaccordance with the invention was determined before and after theapplication of topical fluid repellent. The results set forth in Table 2attached demonstrate the beneficial balance of antistatic and fluidrepellent properties provided by the barrier laminates of the invention.

As indicated in Table 2, the barrier laminates of the invention exhibita beneficial balance of antistatic performance, alcohol resistance andhydrohead.

Handsheet Examples

Comparative Example 6 was prepared by bonding outer layers of 7657Polypropylene Spunbond Filaments (2 to 3 denier) (“SB”) from Amoco Corp.of Chicago, Ill. to an inner layer of 3746 G Meltblown Polypropylene(“MB”) by Exxon Corp. of Houston, Tex. The laminate layers were pointbonded by passing the layers through a heated patterned calender. Atopical fluid repellent was applied to the sample by immersing it intoan aqueous solution containing Bayguard™ LTC, commercially availablefrom Bayer Chemical Corp. of Wellford, S.C., and isopropanol. TheBayguard™ was present in the aqueous solution in an amount of about 2weight percent, based on the weight of the solution (“bos”). Theisopropanol was present in the aqueous solution in an amount of about 4weight percent, bos. The sample was immersed in the topical fluidrepellent for about 2 to 3 seconds until it became saturated. Thesaturated sample was then calendered to reduce the wet pick up oftopical fluid repellent to between 60 to 80% of dry web weight. Thecalendered web was then dried and cured at 265 to 270° F. for 3 minutes.

Example 3 was prepared using the methods and materials of ComparativeExample 6, except that a conductive layer was formed between the bottomspunbond layer and the meltblown layer prior to bonding. The conductivelayer was formed by depositing 1 end of 18 denier No-Shock Grade18-2-E3N from Solutia of Gonzalez, Fla. onto a first spunbond layer toform a 0.23 gsm layer. The conductive layer was then point bonded to thefirst spunbond layer by calendering. The meltblown layer was thenapplied to the conductive layer, and the three layer laminate wascalendered. A second spunbond layer was superposed upon the bondedmeltblown layer and the resulting four layer laminate was calendered toform a barrier laminate in accordance with the invention.

Table 3 indicates the superior static decay time provided by the barrierlaminates of the invention without detriment to the fluid repellentproperties, e.g. the hydrohead and alcohol repellency. As shown in Table3, the conductive layer of the invention may actually increase thehydrohead value of the resulting barrier laminate. Applicantshypothesize that the conductive layer may provide reinforcement for thebarrier laminate, resulting in an increased hydrohead value.

The foregoing examples are illustrative of the present invention and arenot to be construed as limiting thereof. The invention is defined by thefollowing claims, with equivalents of the claims to be included therein.

TABLE 1 Antistatic and Fluid Repellency of Various CommerciallyAvailable Polypropylene SMS Barrier Laminates Topical Alcohol NominalBasis Topical Fluid Hydrohead¹ Repellency² Static Decay Sample SMS IdWeight (gsm) Antistat Repellent (cm) (% Isopropanol) Time (sec)³ Comp.Ex. 1 BBA 55 No No 72 1–2 >60 T0831D Comp. Ex. 2 BBA 55 Yes⁴ Yes⁵ 44 8–90.254 T0832D⁹ Comp. Ex. 3 BBA 50 No No 62 1–2 >60 T0813D Comp. Ex. 4 BBA50 No Yes⁶ 65 8–9 >60 T0813D Comp. Ex. 5 BBA 50 Yes⁷ Yes⁸ N/A 8–9 0.49T0618D ¹Determined per International Nonwovens and DisposablesAssociation (“INDA”) Test Method IST 80.6 (98). ²Determined per INDATest Method IST 80.8 (95). ³Determined per INDA Test Method IST 40.2(92), indicating the average amount of time required for an initialnegative static charge and subsequent positive static charge todissipate from 5000 V to 500 V. ⁴The topical antistat was applied byPrecision Fabric Group (“PFG”) of Greensboro, NC. The composition of thetreatment chemicals are proprietary to PFG. ⁵The alcohol repellant waswas applied by Precision Fabric Group of Greensboro, NC. The compositionof the treatment chemicals are proprietary to PFG. ⁶The fluid repellantwas Baygaurd LTC commercially available from Bayer Chemicals, Wellford,SC, present on the barrier laminate at 1.3 wt %, based on the weight ofthe laminate. ⁷The topical antistat was applied by Precision FabricGroup of Greensboro, NC. The composition of the treatment chemicals areproprietary to PFG ⁸The fluid repellant was Baygaurd LTC commerciallyavailable from Bayer Chemicals, Wellford, SC, present on the barrierlaminate at 1.3 wt %, based on the weight of the laminate. ⁹BBA gradeT0832D is a version of grade T0831D that has been topically treated byPFG for antistat and fluid repellency.

TABLE 2 Antistatic and Fluid Repellancy of Barrier Laminates Formed inAccordance with the Present Invention Static Decay Basis Topical Timefor Weight Topical Alcohol Negative Sample (gsm) Antistat RepellentCharges (sec)³ Example 1 72 No No 0.01 Example 2 72 No Yes⁴ —¹Determined per International Nonwovens and Disposables Association(“INDA”) Test Method IST 80.6 (98). ²Determined per INDA Test Method IST80.8 (95). ³Determined per INDA Test Method IST 40.2 (92), based on timeto dissipate negative charges only. ⁴The fluid repellent was applied byPrecision Fabric Group (“PFG”) of Greensboro, NC. The composition of thetreatment chemicals are proprietary to PFG.

TABLE 3 Beneficial Properties of Comparable Handsheet Samples BasisWeight (gsm) Static Decay Topical Alcohol Time³ Top Conductive BottomAlcohol Hydrohead¹ Repellency² −5 kV to +5 kV to Sample SB MB Layer SBRepellent (cm) (% Isopropanol) −0.5 Kv +0.5 Kv Comp. Ex 6 25 12 0 251.05 64 80 >60 secs >60 secs Example 3 25 12 0.23 25 0.81 79 80 0.010.06 ¹Determined per International Nonwovens and Disposables Association(“INDA”) Test Method IST 80.6 (98). ²Determined per INDA Test Method IST80.8 (95). ³Determined per INDA Test Method IST 40.2 (92), indicatingthe average amount of time required for a negative static charge and apositive static charge to dissipate from 5000 V to 500 V, respectively.

1. A nonwoven barrier laminate comprising (a) outer spunbonded layers;(b) at least one hydrophobic microporous layer between the outerspunbonded layers; (c) at least one discrete conductive layer comprisingelectrically conductive strands, the strands being arranged randomlywithin the conductive layer; and (d) a multiplicity of discrete bondsites bonding together said layers to form a coherent fabric.
 2. Anonwoven barrier laminate according to claim 1 wherein said electricallyconductive strands are selected from the group consisting of carbonfilaments and metallic filaments.
 3. A nonwoven barrier laminateaccording to claim 1 wherein said electrically conductive strandscomprise multicomponent fibers or filaments having at least onenonconductive polymer component and at least one conductive component.4. A nonwoven barrier laminate according to claim 1 wherein saidelectrically conductive strands comprise monocomponent filaments formedfrom a polymer containing a conductive melt-additive.
 5. A nonwovenbarrier laminate according to claim 1 wherein said conductive layercomprises from about 0.1 to 0.5 weight percent of the barrier laminate.6. A nonwoven barrier laminate according to claim 1 wherein saidconductive layer has a basis weight ranging from about 0.01 to 0.5 gsm.7. A nonwoven barrier laminate according to claim 1, wherein saidconductive layer has a basis weight of about 0.2 gsm.
 8. A nonwovenbarrier laminate according to claim 1 wherein said laminate has a staticdecay time of about 0.10 seconds or less for a negative charge todissipate from 5000V to 500V.
 9. A nonwoven barrier laminate accordingto claim 8, wherein said laminate has a hydrohead of at least about 35cm and alcohol repellency of about 6.0 or more.
 10. A nonwoven barrierlaminate according to claim 1, wherein said hydrophobic microporouslayer comprises meltblown fiber.
 11. A nonwoven barrier laminateaccording to claim 1, wherein said spunbond layers and hydrophobicmicroporous layer comprise polypropylene filaments.
 12. A nonwovenbarrier laminate comprising (a) outer spunbonded layers comprisingsubstantially continuous thermoplastic filaments; (b) at least onehydrophobic microporous layer comprising meltblown microfibers betweenthe outer spunbonded layers; (c) at least one discrete conductive layercomprising electrically conductive filaments located between one of saidouter spunbond layers and said at least one hydrophobic microporouslayer, the conductive filaments being randomly arranged within theconductive layer; and (d) a multiplicity of discrete point bond sitesbonding together said layers to form a coherent fabric.
 13. A nonwovenbarrier laminate according to claim 12, wherein said outer spunbondlayers and said meltblown microfibers are polypropylene.
 14. A nonwovenbarrier laminate according to claim 12, wherein said electricallyconductive filaments comprise multicomponent filaments including atleast one nonconductive polymer component and at least one electricallyconductive component.
 15. A nonwoven barrier laminate according to claim12, wherein said outer spunbond layers are treated with a topical fluidrepellant composition.